The aim of this project is to understand the way in which RNA tumor viruses express their genetic information at the transcriptional level. The gene coding for the internal structural proteins of these viruses is located at the 5' end of the genomic RNA and can be expressed directly by translation of genomic RNA. The expression of the genes for the viral glycoprotein (env) and the transforming protein (src) in the avian sarcoma viruses are internal in the genome and their expression is restricted on genomic RNA. It seems probable that these genes are expressed by use of subgenomic mRNAs. We intend to identify the virus specific mRNAs for both avian sarcoma viruses and murine leukemia viruses by in vitro translation in the mRNA dependent reticulocyte lysate. Following identification we will isolate and characterize these mRNAs chemically. For this purpose we will translate both RNA extracted from virions and purified intracellular virus specific mRNAs isolated from infected cells. The products of in vitro translation will be characterized by peptide mapping, two-dimensional gel electrophoresis and immunoprecipitation. We will use conditional and deletion mutants to help in the identification of specific viral gene products. The cap structures, base modifications and ribosome binding site sequences of viral mRNAs will be examined. We will pay particular attention to viral mRNAs for the internal viral genes which may be subgenomic in size. By these methods we hope to identify the mRNA and the product of the src gene of avian sarcoma viruses. If we can identiy an in vitro product from the src gene, we will attempt to localize the transforming protein in cells transformed by an avian sarcoma virus and to isolate this protein. Then we will begin to define the way in which its interaction with the cell causes malignant transformation.